Eye examinations are widely performed for the purpose of early diagnosis and treatment of lifestyle-related diseases and diseases which are the leading causes of blindness. Ophthalmic equipment used for eye examinations includes a scanning laser ophthalmoscope (SLO), serving as an ophthalmic apparatus based on the principle of a confocal laser scanning microscope. The scanning laser ophthalmoscope is an apparatus (hereinafter, referred to as an “SLO apparatus”) that scans a laser beam, serving as measurement light, over a fundus in a raster pattern and quickly obtains a high resolution planar image based on the intensity of return light associated with the measurement light.
It has recently been possible to acquire a higher resolution planar image of a fundus by increasing the beam diameter of measurement light in the SLO apparatus and significantly reducing the size of a spot of the measurement light on the fundus. In acquiring a planar image of the fundus, however, the signal-to-noise (S/N) ratio and resolution of the planar image are reduced due to aberrations of measurement light and its associated return light caused in an eye to be examined by an increase in beam diameter of the measurement light.
The reduction of the S/N ratio and the resolution is countered by measuring the aberrations of the measurement light and the return light caused in the eye to be examined in real time using a wavefront sensor and correcting the aberrations in the eye to be examined using a wavefront compensation device. An adaptive optics SLO apparatus (hereinafter, referred to as an “AOSLO apparatus”) including an adaptive optics system, such as a wavefront compensation device, has been developed to enable acquisition of high resolution planar images.
To acquire a high resolution planar image, the beam diameter of measurement light is increased in the above-described confocal optical system. In some cases, the confocal optical system is allowed to include a non-confocal optical system depending on a region or tissue of a fundus, whose image is intended to be acquired, in order to increase the S/N ratio of a planar image.
NPL 1 describes an AOSLO apparatus having a configuration for increasing the S/N ratio of a planar image (blood vessel image) to be acquired. Specifically, return light from a fundus is split into two beams on an imaging plane of the return light and the beams are allowed to enter different optical sensors such that the sensors detect the beams. Signals from the optical sensors are subjected to calculation (subtraction) to form an image of a retina.
PTL 1 describes a configuration for forming an image of a very small biological substance. Specifically. PTL 1 describes that the shape of a pinhole in an optical sensor for receiving return light from a fundus is changed in order to acquire high resolution planar images of various regions and tissues of the fundus.